1. Field of the Invention
The present invention relates to a recording head of an ink-jet recording apparatus for OA machines or the like. Particularly, the present invention relates to an ink-jet recording head comprising a recording device substrate for discharging a recording liquid fitted to a flexible film wiring substrate. The present invention relates also to an ink-jet recording apparatus employing the ink-jet recording head.
2. Related Background Art
The ink-jet recording apparatus, which conducts recording by a non-impact recording system, has advantages of high speed recording, suitability for various recording mediums, and less recording noise generation. Therefore, the ink-jet recording is employed widely in recording mechanisms of various machines such as printers, word processors, and copying machines.
The ink-jet recording conducts recording by discharging fine liquid droplets through a discharge opening onto a recording medium like a paper sheet, typically employing an electrothermal converting element. The ink-jet recording apparatus is constituted generally of an ink-jet recording head having a nozzle for forming liquid droplets and an ink-supplying system for supplying the ink to the head. In the ink-jet recording head employing an electrothermal converting element, the electrothermal converting element is provided in a pressurizing chamber. An electric pulse as the recording signal is applied to the electrothermal converting element to give thermal energy to the recording liquid. The phase change of the recording liquid due to thermal energy causes bubbling (or boiling) of the recording liquid, and the pressure of the bubbles forces the recording liquid to eject.
The ink-jet recording heads employing the electrothermal converting system are classified into two types: an edge shooter type which discharges the recording liquid in the direction parallel to the substrate having electrothermal converting elements arranged thereon, and a side shooter type which discharges the recording liquid in the direction perpendicular to the substrate. The constitution of the ink-jet recording head is described specifically by reference to the side shooter type recording head.
FIG. 10 is a perspective view of a side shooter type recording head.
Plural discharge openings 202 are formed for discharging ink at the central portion on the front side of a recording device substrate 201. On the reverse side of the substrate, an ink-supplying opening 203 (broken line in the drawing) is formed in a length nearly equal to the length of the row of the discharge openings. Although several discharge openings are shown in FIG. 10, several tens or several hundreds of discharge openings are provided in a practical recording device substrate.
For ink discharge, electrodes on the recording device substrate 201 are electrically connected to electrode terminals of a flexible film wiring substrate 204. The input terminals of the flexible film wiring substrate 204 are electrically connected to output terminals of a wiring substrate 206 having external input pads 205 for supplying electric signals of recording information and the like to an ink-jet recording head from an ink-jet recording apparatus body. The numeral 212 indicates an ink supplying-holding member.
FIG. 11 shows specifically a structure of the recording device substrate and the flexible film wiring substrate. FIG. 12A and FIG. 12B show the state of the recording device substrate fitted to the flexible film wiring substrate: FIG. 12A is a perspective view showing the state, and FIG. 12B is a sectional view taken along the plane 12B in FIG. 12A.
In FIG. 11, electrodes 210 are formed on a recording device substrate 201 for connection with output terminals of a flexible film wiring substrate 204. The electrodes 210 are usually formed in rows on the end portion of the surface of the recording device substrate 201. The electrode formation can be conducted by a conventional technique such as plating by patterning, and ball-electrode formation by wire bonding (stud bump).
The flexible film wiring substrate 204 has an aperture which uncovers the orifice face 207 having discharge orifices 202 when the recording device substrate 201 is fitted thereto. In this aperture, electrode terminals 208 are provided for connection with the electrodes 210 on the recording device substrate 201. The electrode terminals 208 of the flexible film wiring substrate 204 are connected with the electrodes 210 of the recording device substrate 201 by ILB (inner lead bonding) of the terminals of TAB (tape automated bonding).
The recording device substrate 201 is fitted to the flexible film wiring substrate 204 as shown FIGS. 12A and 12B such that the electrodes 210 of the recording device substrate 201 are connected to the electrode terminals 208 of the flexible film wiring substrate 204 and the orifice face 207 is fitted to the aperture of the flexible film wiring substrate 204. To prevent corrosion of the electrodes and underlying metallic materials thereof by deposition of splashed liquid droplets from the discharge opening or by repelled ink from a recording medium, the electrode portions are coated and sealed with a sealing material 211 such as an epoxy resin which has sufficient sealing and ion-intercepting properties. In this structure, the recording liquid is supplied from an ink supply opening 203 to an ink flow path 209 communicating with ink discharge openings 202, and liquid droplets are discharged through the discharge openings 202.
In recent years, with the progress of ink-jet recording head in high speed recording and multi-color recording, an ink supplying-holding member (212 in FIG. 10) has come to be employed which holds plural flexible film wiring substrates 204 holding plural recording device substrates. In such a case, as shown in FIG. 13, the input terminals 204' of the flexible film wiring substrate 204 are connected to the output terminals 206' of the wiring substrate 206 by solder 213, and a flux is used as an active agent for removal of an oxide film and stains.
The above-mentioned ink-jet recording head has problems of low printing quality and low reliability as described below.
(1) The flexible film wiring substrate is connected with the wiring substrate by use of solder, and an oxide film or a stain is removed by a flux. It causes splashing of flux during the soldering to cause clogging of the discharge opening of the recording device substrate to lower the print quality.
(2) A flux residue 211 as shown in FIG. 13 after the soldering generates an ionic gas. The gas molecules adhere to the periphery of the discharging openings to lower the ink-repellency, or permeate into the discharge openings and adheres to the electrothermal converting elements to lower the electrothermal conversion efficiency, which lowers the printing quality.
(3) The process for coating the electrode portion with the sealant in connection of the recording device substrate 201 with the flexible film wiring substrate 204 requires generally a counter measure against heat. A volatile low molecular component or solvent in the sealant may adhere the orifice face, nozzle inner walls, and electrothermal converting element surfaces during the curing of the sealant, which changes the wettability of these portions to the ink to deteriorate remarkably the printing quality.
(4) The sealant for the electrode portions of the recording device substrate 201 and of the flexible film wiring substrate 204 will protrude from the orifice face 207. The distance between the head and the recording medium should be made larger corresponding to the protrusion.
(5) The aforementioned protrusion may cause trouble in wiping of the orifice face 207 by a rubber blade in removing ink droplets and dusts such as paper powder therefrom. This results in adverse effects on printing quality.
(6) The inner lead bonding (ILB) by tape automated bonding (TAB) requires a high temperature above 350.degree. C. or a supersonic working for metallic bond formation, which may cause deterioration of the nozzle member material, weakening of the adhesion between the orifice face and the underlying face, and lowers the reliability of the nozzle, thereby lowering the printing quality.
(7) In the ILB bonding by the TAB method, the plural rows of electrode terminals 208 cannot readily be arranged close to each other on the flexible film wiring substrate 204. This makes difficult the increase of arrangement density of the electrode terminals 208, or the connection density between the electrodes 210 of the recording device substrate 201.